Plastic containers such as bottles of water are manufactured and filled according to different methods including blow moulding or stretch-blow moulding.
According to one of these known methods a plastic preform is first manufactured through a moulding process and then heated before being positioned inside a blowing mould.
The preform usually takes the form of a cylindrical tube closed at its bottom end and open at its opposite end.
Once the preform has been positioned within the mould only the open end of the preform is visible from above the mould.
The above-mentioned method makes use of a stretch rod which is downwardly engaged into the open end of the preform so as to abut against the closed bottom end thereof. The stretch rod is further actuated to be urged against the closed end, thereby resulting in stretching the preform.
After the stretching phase has been initiated a liquid is injected into the preform through its open end during a filling phase, as disclosed for instance in Applicant's patent EP 1 529 620 B1. This liquid injection causes expansion of the preform until coming into contact with the inner walls of the mould, thereby achieving the final shape of the bottle.
The Applicant has noticed that at the end of the filling phase when liquid injection is stopped, a back pressure occurs in the pressurized liquid injection circuit due to the nearly incompressibility of liquids.
This back pressure phenomenon causes mechanical stresses and possibly damages to different components which are used in connection with the liquid injection circuit.
More particularly, the above-described blowing and filling method makes use of a piston device for pushing the liquid throughout the liquid injection circuit for its injection into the preform.
Filling of the preform with liquid is performed and requires deceleration of the filling pace at the end of the filling phase.
However, control of deceleration proves to be very difficult with today hydraulic, pneumatic or electric technology.
In particular, due to inertia the piston device is always moving beyond the requested stopping point.
As the liquid is nearly incompressible, this results in a high pressure of liquid, thereby giving rise to the back pressure phenomenon within the liquid injection circuit.
The mechanical components which are in connection with the liquid circuit are thus submitted to mechanical stresses due to back pressure.
These stresses and their impact on the components repeat over time, which therefore leads to a reduced life time of these components.
Also, an inefficient control of liquid filling deceleration may lead to breakage of the container.